The invention relates to glide heads for evaluating the glide quality of a disc surface, and to related methods. More particularly, the invention relates to glide heads that detect vibrations resulting from collisions of the slider with a defect on a disc surface.
Disc drives are used for storing information, typically as magnetically encoded data, and more recently as optically encoded data, on a disc surface. Glide tests are used to check disc surfaces for defects. Glide tests allow computer disc manufacturers to control and assure the quality of the disc media. Generally, all hard drive discs are tested before shipment. During a glide test, the glide head or slider flies over a disc surface generally at a predetermined clearance from the disc surface, known as the glide height or fly height.
If contact occurs between the glide head and a disc defect or asperity, the glide head vibrates and deforms. The vibrations can be measured with a piezoelectric transducer (PZT), which generates a potential difference between the electrodes of the PZT due to deformation of the transducer. Specifically, when the glide head interacts with a defect on the spinning disc, simultaneously excited vibrational modes of the PZT and the head result in voltages at corresponding frequencies. If the magnitude of measured voltages exceed predetermined threshold values, the disc may be rejected.
As storage densities on disc recording media become larger, fly heights of read/write heads generally become smaller. Lower fly heights impose narrower restrictions on acceptable magnitudes of defects on a disc surface since higher defects are more likely to result in contact between the read/write head and the disc. Contact between a read/write head and a disc generally results in damage to the head and/or to the disc. The glide quality of a disc directly relates to the ability of a head to fly adjacent the disc at a fixed distance from the disc without colliding with a significant defect on the disc that results in deformation of the head with a magnitude above a threshold value. The glide quality of a disc is related to the disc smoothness, although other defects also may alter glide quality.
As the tolerances on the disc smoothness (glide quality) decrease, glide heads must fly correspondingly closer to the disc surface in order to measure defects with elevations matching or exceeding the tolerance levels. Glide heads generally are designed to have a fly height that is sensitive to the linear velocity of the disc surface relative to the glide head. To achieve detection of smaller asperities on the disc surface, the disc velocity can be decreased to decrease the fly height of the glide head.